1. Field of the Invention
This invention relates to a flat keyboard switch of the type which has a built-in light emitting element for illuminating a switching section.
2. Description of the Related Art
Flat keyboard switches of the type mentioned above are already known. An exemplary conventional flat keyboard switch is shown in FIGS. 1 and 2 which are a partial sectional view and a partial plan view with a surface sheet, respectively.
The conventional flat keyboard switch shown includes a pair of fixed contact elements 15 and 16 provided on a surface of printed circuit board 14 and diaphragm 13 in the form of a semi-spherical metal spring plate disposed as a movable contact on fixed contact element 15 above fixed contact element 16, thereby constituting a switching section.
Surface sheet 11 is provided to isolate and protect the switching section from the outside, and movable element 18 in the form of a plate is disposed between surface sheet 11 and diaphragm 13 such that, when the switch is depressed, the depressing force is transmitted to diaphragm 13 by way of surface sheet 11 and movable element 18 to deform diaphragm 13 downwardly into contact with fixed contact element 16 to establish electrical connection between fixed contact elements 15 and 16 by way of diaphragm 13. Movable element 18 is provided in order to provide a definite click feeling by a turning over operation of diaphragm 13.
Indicium 19 such as a graphic pattern or figure or a character is printed at a portion of surface sheet 11 above movable element 18 as seen in FIG. 2. Indicium 19 is printed as a white-on-color representation from transparent or color ink having a light conducting property so that light from the rear or lower face of surface sheet 11 may be introduced to the upper face of surface sheet 11. Light emitting element 17 is disposed on printed circuit board 14 in the neighborhood of diaphragm 13.
Light emitted from light emitting element 17 is introduced to a location near diaphragm 13 by way of light emitting plate 12 in the form of a transparent flat plate provided on printed circuit board 14 and adapted to transmit light therethrough. Then, the light is scattered toward movable element 18 made of a material having a light conducting property. The light scattered to movable element 18 thus illuminates indicium 19 on the surface sheet 11 from the rear side.
The conventional flat keyboard switch described above is disadvantageous in that the assembling step in manufacture is complicated because it includes movable element 18 which is formed as an independent element.
Further, since movable element 18 and light transmitting plate 12 do not make a continuous structure but are formed as mutually independent elements with a spacing left therebetween, light emitted from light emitting element 17 and introduced by light introducing plate 12 is scattered while it passes the spacing between movable element 18 and light transmitting plate 12. Consequently, the conventional flat keyboard switch is also disadvantageous in that light emitted from the light emitting element is not utilized efficiently for the illumination and indicium 19 on surface sheet 11 may not be illuminated with sufficient light.